1. Field of the Invention
The present invention relates to an analog subscriber circuit, comprising an electronic switching system on-hook transmission function.
2. Description of the Related Art
As a service targeted at an analog user in an electronic switching system, there is demand for a Calling Line Identification Presentation (CLIP) service in accordance with an on-hook transmission function.
A CLIP service is a function, which sends to an on-hook transmission-capable subscriber terminal from an electronic switching system the number of a calling party and other information data, which is displayed on the subscriber terminal in the subscriber circuit non-feed state of the silent state between rings during ringing processing.
This kind of CLIP service has been provided for digital circuits for some time. In recent years, the same service has begun to be offered for analog circuits as well.
In particular, telephone service rate systems differ according to region (country). In some regions, only the calling party pays the charges, and in other regions, both the calling party and the called party pay charges. The need for the CLIP service is especially high in regions, which use the latter rate system.
This is because it is possible, in accordance with a CLIP service, to confirm incoming calls from high toll charge portable telephones, and incoming calls felt to be unnecessary. In accordance therewith, it is possible to reduce telecommunications expenses by selecting and receiving only necessary incoming calls.
Therefore, the CLIP service has become common in recent years, and is provided as a standard function of recent switching systems. However, to realize this CLIP function, the following functions are required in addition to the ordinary functions of an analog subscriber.
First, an on-hook transmission (OHT) function is required.
An OHT function is a function, which realizes a one-way call from a subscriber circuit to a terminal in the non-feed state in which there is no speech current when the subscriber terminal is in the on-hook state (the telephone handset is resting in its cradle).
When a subscriber terminal, which is connected to the battery feed circuit composed of non-mechanical electronic components in an analog subscriber circuit, is in the on-hook state, the output of the line B battery feed circuit extends to the ground potential, and the output of the line A battery feed circuit extends to VBB. Therefore, since clamping occurs if a voice signal attempts to pass through in this state, this function applies a bias to both the line B battery feed circuit and the line A battery feed circuit to prevent such clamping.
Second, a function is required for increasing power when CLIP is requested. An ordinary analog subscriber circuit monitors whether the subscriber terminal is in the on-hook state, or in the off-hook state (state in which the handset is removed from the cradle). When the subscriber terminal is in the on-hook state, power to a coder-decoder circuit (CODEC) is decreased for the purpose of cutting down on current consumption.
However, in order to utilize the CODEC to send a voice signal when there is a CLIP state request from the system, the power to the CODEC must be increased even if the subscriber terminal is in the on-hook state.
Therefore, a CLIP request interface is provided between an analog subscriber circuit and the system, and when a CLIP request is sent from the system, the analog subscriber circuit switches the battery feed circuit to the OHT mode, and increases power to the CODEC. However, there are numerous problems involved in providing a CLIP service in an old-fashioned switching system (a switching system designed before the CLIP service was available). When, in accordance with a customer request, an analog subscriber circuit is upgraded or replaced for the purpose of providing a CLIP service in an old-fashioned switching system, the problems set forth hereinbelow occur.
When attempting to upgrade to a CLIP function-equipped subscriber circuit designed for a switching system premised on the provision of a CLIP service, it is necessary to provide a new CLIP function control hardware-based interface with the host system of the subscriber circuit. As a result, the existing system must undergo major modifications.
Moreover, even if a hardware interface is provided with the host system, because the host system does not take CLIP service processing into consideration, the analog subscriber circuit does not process CLIP control fast enough.
Therefore, to enable the provision of a CLIP service even without host system control, based on a CLIP function-equipped subscriber circuit designed for a switching system premised on the provision of a CLIP service, steps were taken to design a subscriber circuit, which is constantly in the OHT mode (battery feed circuit is normally in the OHT mode, and the CODEC is constantly being powered up). However, this gave rise to the following problems.
Because the CODEC is constantly being powered up, the current consumption of the subscriber circuit increases. And because the battery feed circuit is normally in the OHT mode, the open loop voltage between the A and B lines of the subscriber circuit decreases when the subscriber terminal is on-hook, causing the subscriber terminal, which monitors the voltage of the subscriber line, to malfunction.
Since the battery feed circuit is normally in the OHT mode, sufficient current cannot be supplied to a long-distance distance subscriber terminal due to the decrease of speech current when the subscriber terminal is off-hook. Accordingly, long-distance subscribers capable of being accommodated up until now can no longer be accommodated.
An object of the present invention is to solve the above-mentioned problems by providing a subscriber circuit capable of realizing a CLIP service in a conventional switching system.
More particularly, an object of the present invention is to provide a new CLIP function-equipped analog subscriber circuit, comprising a control circuit which autonomously detects ringing, and the silent state between ringing, and sets the battery feed circuit to the OHT mode, and increases power to the CODEC during the silent state thereof in order to solve for the above-mentioned problems.
An analog subscriber circuit for achieving the above-mentioned tasks in accordance with the present invention is an analog subscriber circuit for use in a switching system, which supplies a ringer signal to a subscriber line via a ringer relay, and the analog subscriber circuit includes a timer, which commences timer operation when the recovery of the ringer relay is detected, and terminates the timer operation at a predetermined time, a battery feed circuit supplying speech current to the subscriber line via the ringer relay when a subscriber terminal is in an off-hook state, and a circuit, which controls the bias voltage of said battery feed circuit to the ON state during the operation period of the timer.
As one mode, the above-mentioned analog subscriber circuit is characterized in that it has a loop detecting circuit, which also detects when a telephone terminal is off-hook, and the above-mentioned timer is reset by the loop detecting circuit in accordance with detecting that the above-mentioned telephone terminal is off-hook.
As yet another mode, the above-mentioned analog subscriber circuit is characterized in that the above-mentioned timer can be set to an arbitrary timer time.
As one specific constitution, the above-mentioned analog subscriber circuit has a ringer transmitting circuit, which is connected to line A line and line B, and which transmits a ringer signal in accordance with a ringer transmission request signal from the host system, a battery feed circuit, which supplies speech current to the line A and line B, and a timer, which, in accordance with a change in the level of a ringer transmission request signal from the above-mentioned host system, detects the end of transmission of a ringer signal sent by the ringer transmitting circuit, starts timer operation, and, after the passage of a predetermined period of time, terminates this timer operation, and the analog subscriber circuit is characterized in that it is constituted so that a speech current is supplied to this line A and line B from the above-mentioned battery feed circuit during the above-mentioned timer operation period.
Further, the above-mentioned specific constitution is characterized in that it also has a CODEC, which converts subscriber information data from the above-mentioned host system to an analog signal, and power to this CODEC is increased during the above-mentioned timer operation pFXfF period.
The characteristics of the present invention are further clarified from the aspects of the embodiment of the invention, which are explained hereinbelow in accordance with the figures.